I'm sorry for your loss. It's hard losing those we love.
16 years is a long time to love then lose.
I'm sure you gave your cat a good life.
My sister takes in old abandoned cats from the local shelter. They have often been strays for a long time.
She knows they won't live long. The last one had kidney problems, had lost an eye, probably in a fight and he only lived 10 months after she got him. He was very old, very loving and grateful having a home again.
She grieves every one when they pass.
Be glad you gave your cat a loving home for 16 years. Lots are not that lucky.